Selecting system



Oct. 13; 1942. N. l. HALL sELEcTINGsYsTEM Filed Feb. 8, 1941 :s sheets-sheet l 'TIME /VVENTOR By N. HALL ATTORNEY 'Octj.l1"3, 1942. Y l N. l. HALL v 2,298,695!

.s'ELEcTING SYSTEM Filed Feb. sl', 1941 s sneet-sheet 2 F/aj 2 v I /NVENTOVR N HALL N. l. HALL 2,298,695

- SELECTING SYSTEM Filed Feb. .8, 1941 3 Sheets-Sheet 5 l l. I'. l 'v'=. i A l /NVE/v fof? N HLL ATTORNEY Patented :Oct 13, 1942 N y 2,298,695- v UNITED STATES vPATENT OFFICE l i 2,298,695 l u sELEc'rmG sYs'ruM i Nathan I. Hall, Long Island City, N. Y., wither to Bell Telephone Laboratories, Incorporated,

New York, N. Y.,l a corporation o! New York Application February s, i941, serial No. 377,995

' 1oV claims. (ci. 17a-41s) This-invention relates to selecting systems and particularly to systems in which the selective operations are performed automatically.

An object of the invention is to control the propagation'of electric waves and to utilize-these waves for selecting lines, trunks or other electrii cal circuits or devices. 4

Another object-.is to obtain greater uniformity in the rate at which these waves are propagated and consequently greater accuracy in the selecting operation.

Another object is to obtain a more useful spacv ing of the voltage values along the circuit on which thewaves are propagated. y

Another object is to simplify and otherwise to improve voltage controlled selecting circuits.

In accordance with this invention the foregoing and other objects 'are realized by means of a shunt to the common condenser. When so connected the common resistance shunts some of the current flowing through the series resistors, the

the charging of the condenser, of the total cur` selecting system in which the lines, trunks, circuits or other devices of a group aretested' in succession by aseries of space-discharge devices or tubes which. are rendered effective successively by propagating a voltage wave along an electric circuit and utilizing the progressing wave to io'nize the tubes one after another. The tubes are connected respectively to the lines or other devices being tested; and, when each tube in'turn is ionized by the voltage wave. aitest is made of `the associated line to determine its condition.

When the iirst idle line is reached by thisprogressive test, the 'corresponding tube discharges, the line is chosen, and the remaining tubes are by preventing the testing and selection of a second line in the group. i

A feature of the invention is a selecting system in which the voltage-propagationfcircuit includes a-plurality of resistors, one for `each tube,

connected in lseries with each other and in series withfa common condenser. LWhen the sourceof voltage is connectedto this circuit, current ilows l through'all'of the resistors in' series to charge `the condenser. As the condenser charges a voltageof a predetermined value moves along the circuit from one resistor to the next,` ilnallyreaching the condenser. If the resistors are chosen at substantially equalvalues, the differences in voltage between successive resistors along the .circuit will be substantially equal. This means that the successive tubes will receive their operating voltages consecutively and that 'no ltube will be permitted to operate until after operating voltage hasbeen applied to the preceding' tube.v V

Another feature is a voltage propagating cirrendered unresponsive to the voltage wave, thereelements, such as resistances.

remainder of this current serving to charge the condenser. Hence the rate of change, cause by rent flowing through the series resistors is reduced by the presence of the shunt resistor. This increases correspondingly the time intervals requiredlfor the voltage wave-to "move from one tube tothe next, the maximum effect taking `place in the sections nearest the condenser where the voltage and time differences` between sections tend to be smallest. These increased intervals are highly desirable since they ailord adequate time foreach tube to function before full operat-V l ing voltage is applied to the succeeding tube. y

These and other features of the invention will be discussed more fully in the following detailed specification.

tion:

ing certain features of the present invention;

Figs. 2, and 3 disclose a testing and selecting vsystem incorporating the voltage propagating cifvadvantages which detract from their effectiveness when employed for selecting voltage oper-A ated devices. For example, it is diicult in these prior systemsto maintain uniform differences of voltage along the propagation circuit. In other words, the differences lbetween successivepoints in one part of the circuit are less than thoseexisting between corresponding points in another part of the circuit. 'Again it is difficult toobtain a uniform time rate of changeof voltage alongl the propagation circuit.V That isto say, the in terval required for the voltage to rise to a given value at one point following the instantv it reached said value at lthe preceding point in 'the circuit will varyin diierent parts of the circuit. Withl 4these `disadvantages in a voltage propagating circuit it1 follows that responsive devices, such as space-discharge tubes, may operate falsely'either because the voltage differences between successive f cuit in which a common resistoris connected in l .tubes 'are-not sumcient to insure the proper se-iv In the drawings accompanying the specicaf Fig. 1 is a Voltage propagating circuit includ-v quence of operation or because the rate of propagation of theoperating voltage is sol rapid that one tube in the series does not have sulcient time in which to operate before the operating voltage is applied to the next succeeding tube.

These advantages are overcome in the present system by means of the voltage propagating circuit above mentioned, which includes a single condenser connected in series with a plurality of resistance elements and a shunt resistance connected across `the common condenser. The advantage of this circuit, as will be explained more fully hereinafter, is that a substantial voltage difference is maintained between all sections of the circuit and thatthe rate of propagation of the voltage wave is substantially uniform in all parts thereof.

Referring to the drawings, and first to Fig. l, the voltage propagation circuit comprises a plurality of resistors R1, Ra, Ra, R4, R Re and Rio, a condenser C, and a shunt resistance Rn connected across the terminals of the condenser C. While there may be any desired number of resistance elements in the series, it is as sumed in the present disclosure that there are ten of these elements. The values of the resistors R1 to R10 may be chosen to obtain the desired relation between the voltages present at the successive junction points III, H2, H3, H4, IIB, |I0 and |20. Since the' voltages at these junction points are'utilized to operate voltage responsive devices |0|, |02, |03, |04, |05, |09 and ||0 it is desirable to maintain a substantial difference between the voltages at any two junction points, particularly as these voltages approach the-value at which the responsive devices operate. The reason for maintaining a definite spacing of the voltage values from one resistance to the next is to enable the selection of any one of the voltage operated devices by testing these devices in sequential order. In particular, if the voltage operated devices I0| to Ill, inclusive, are space-discharge tubes, it is desirable to maintain a certain difference of voltage between consecutive tubes so that the voltage applied to any tube is well below the operating valuevat the time operating voltage is being applied to the adjacent tube. For example, at the instant the voltage at the junction point ill reaches the operating value of the tube |03 the voltage of junction point lll should be suiliciently less than the operating value of tube |04 to insure against the false operation ofthe latter tube. This dlerence ofyvoltage depends, of course, upon the value of resistance R4 and the value of the current flowing therethrough at the time.

" Since it may be assumed that the operating voltages or the devices m to m win m actual practice vary substantially, it is important that the voltage differences between successive devices should be maintained at a value suiiicient to insure against .false operation. With this end in view good results may be obtained by assigning regard to the voltage of the source |2| and the operating voltage of the responsive devices. If, for example, the operating voltage of the devices III to ||0 is substantially less than the full voltasaaeas make resistor Ri high as compared with the resistors Ra to Rio in order that the voltage applied to the responsive device |0| be somewhat below its operating value the instant after relay 822 is operated.

The purpose of the condenser C is to produce a diminishing now of current in the circuit |00 following the closurev of the relay switch |22.

. Upon the closure of this switch current flows through the resistors R1 to Rio in series, whereupon it divides, part of it flowing into the condenser C, and the remainder flowing through the common resistor R11. At the first instant following the closure of the circuit, condenser C being fully discharged, current of maximum value flows through the series resistors, and voltages of minimum values appear at the successive junction points ||I, H2, H3, etc. However, as the condenser C accumulates its charge-the current flowing in the circuit diminishes correspondingly, and the voltages at the successive `iunction points rise correspondingly. In effect, therefore, a volt l age wave progresses along the series resistors, increasing at the successive junction points as the condenser C becomes charged. A voltage'amplitude necessary to operatethe responsive devices reaches the junction point shortly after the circuit is clozed and progresses from one resistor to the next until it nnally reaches the junction point |20 shortly before condenser C assumes its fully charged condition. Since the resistors Rz to Rm are equal in value a substantially equal voltage difference is maintained between junction points for different values of current flowing in the circuit. Although this voltage difference decreases as the condenser C charges, it is maintained sufficiently high by selecting the proper value for the series and shunt resistors to insure against false operation of the voltage responsive devices.

The common resistor R11 plays an important part in the voltage propagating circuit in that it approximately equalizes the voltage and time spacingin the various sections. Without resistor Ru the voltage and time differences between sections of the circuit decrease as the wave approaches the condenser. However, resistor Rn limits the final condenser voltage and thereby reduces the charging rate, the effect becoming greater as the charge increases. This in turn l increases the voltage and time spacings in the age of the battery |2I, it may bc necessary to 75 end sections, and the result of these two opposing factors is that the spacing is nearly uniform in all sections of the circuit.

The effect of the common resistor R11 on ther end section may be seen more clearly from the graph of Fig. 4. In the figure the curves en and ero represent the voltages at the junction points H9 and |20, respectively, when the common resistor Rn4 is omitted. 'I'hese voltages increase with time until they reach the limiting value of the circuit. -As these curves reach the ordinate value '70, which may be assumed to be the loperating voltage of the responsive devices |09 and H0, they are separated by-a time interval represented by the horizontal line t1.' When, however, the commonresistor Rn is added, the

increasing the time spacing from t1` to t: is that a longer interval is afforded for one voltage responsive device to operate before operating volt-f' age is applied to the next succeeding device.

It will be noted vthat resistors Riz, R13, R14, R13, Rza-Rza, R21 are included in circuit with responsive devices to ||0. These resistors serve toV prevent lockouts or other interference with the operation of the responsive devices, particularly when discharge tubes are used.

Referring now to Figs. 2 and 3, a description will be given of the invention when applied to a system for testing and' selecting lines, trunks or Y other circuits. Two groups of lines 200 and arel illustrated. The lines of these groups may be selectedby corresponding switches 202 and 203, which may be switches of the well-known cross-bar type, or of any other type, to extend connections from incoming lines, such as the lines 204 and 206. The lines of the groups 200 and 20|, and other groups not shown, are tested and 320 ofthe discharge tubes 30|, 302, 303, 303

and 3|0 of the group 360. The cathodes 32|, 322, 323, 329 and 330 of these tubes are connected to the common cathode conductor 304.- The anodes 33|, 332, 333, 333 and 340 of said tubes that the control grid 34| is connected over conductor 321 through the connector 333, conductor 323to the test conductor 203 of the nrst line 2 01 of the group 200. If this line 201 is busy'. it has the usual ground potential thereon, which may be applied from the closed contacts of relay 2|4 through ythe contacts of switch 202 tothe test conductor 203. This ground potential is extended over the conductor 323 through contacts of connector 306 and over conductor 321 to the control grid 34| of the tube 30|. Therefore, the ionization does not transfer to the main fanode 33|, and no current flows in the anode circuit to operate the relay 3|4 individual to this particular tube. A moment later the voltage of junction point .H2 rises vto a value such that the voltage applied across the `starting gap 3|2--322 is sumcient. to ionize the tube 302. Similarly, if the second line 203 is busy ground potential appears on the control grid 342, and the tube 302 fails to discharge.

Assume, however, that the next line 209 is idle. Therefore, battery potential is applied from the positive pole of battery 2|0 through the winding 'of magnet 2||, test conductor 2|2, conductor 2|3, connector 306, conductor 334 to the control grid 343 of the tube 303. When, therefore, the voltage of the junction point ||3 rises to the proper value and the starting gap 3|3-323 ion'- izes, the tube 303 discharges its main gapand current iiows from the positive pole of battery 305 through the winding of relay 3|6, anode 333, cathode .323, conductor- 304, contacts of relay 303, common resistance 325 to the negative pole of battery y324. Relay 3|6 operates in this circuit to register the idle condition of the line 209 are connected through the respective registerv relays 3|4, 3|5, 3|3, 3|1-and 3 |3 to the common source of anode supply voltage 305.' The control grids 34|, 342, 343, 343' and 350 of the tubes 30|,

302, 303, etc., are connectable to the test conductors of the groups of lines` 200, 20|, etc., undergoing test. j

A connectorv .303 is provided for the purpose ofvconnecting the common testing and controlling in the'group 200. The ilow of current in the common resistor 325 .alters the potential of the cathodes ofall of the remaining tubes in .the

group 360 so that none of these tubes will ionizea its starting gap in response to the voltage wave mechanism 300 to the desired group of lines. In

any well-known manner the connectorl 306 may be operated at the desired time to connect the control grids of theseries of tubes 360 to the test or sleeve conductors ofthe desired group, such as the group 200. A

Following the operation of the connector 303 to connect the tubes 360 to the lines of the desired group 200, or at any suitable previous time, the

relay 303 is operated to connect the negative pole of battery 324 through resistor 325 to the common cathode conductor 304. Also at any suitable time relay 301 is energized to close the voltage propagating circuit |00, and current ows through the series resistors R1, Rz, R3, etc., and

into condenser C and through the common resistor Ru. As soon as current begins to flow in this circuit a `positive potential appears at the junction point which fis added to the voltage of battery 324 to produce a voltage difference across the starting gap 3| liv-32| of the first tube '30|. As the condenser C vcontinues to charge the voltage of the junction point continues to rise untill the voltage across the starting` gap of the tube 30| reaches the ionizing value.

Thereupon the starting gap ionizes, the tube is now in condition to transfer its ionization to the main anode 33| providedthe proper potential exists on the control grid 34|. It will be noted as it progresses along the circuit |00. Hence the rst idle one of the lines in the group 200 is selected, and the remaining lines are protected against selection by rendering the tubes 360 unresponsive to the voltage wave. The 'operated relay 3|6, identifying the selected line 203, may' serve in any well-known manner to cause the operation of switch 202 to seize the selected line. "In case all lines in the group 200 are found -busy when the test iscompleted the circuit will wait until one of the lines subsequently becomes qidle, after which the tube assocated with this line immediately operates.

After the line has been selected and the switch 202 operated, or when the allowable time for testing has expired without finding an idle line,

theconnector 306 may be released to free the common mechanism 300 for use in testing other groups oi lines. l

A still further improvement in the time and voltage characteristics `oi? the propagating circuit |00 may be had by connecting an inductance |06 of suitable value in parallel with the resistor R1 as indicated in Fig. 3. When lthe circuit is first closed the inductarce |06 presents a high impedanceso that the value of the current which flows at`the time of circuit closure depends upon the resistances in the circuit. However, as the rate of change of currentdiminishes with the charging of condenser C the inductive impedance of the element |06 correspondingly diminishes, and, since the resistance of this element is low when .compared with the resistor R1, more and more current is permitted to flow in the circuit |00. 'I'his increasing-rate of current now due to the decreasing impedance of the path through the element l06 serves to compensate for the condenser charging component, which becomes less and less as the condenser assumes its full charge. Therefore, the rate of change of the total current owing through the series resistors is reduced correspondingly with the result that the voltage separation between successive resistors and the time rate at which the voltage wave is propagated are both improved substantially.

While the voltage propagating circuit has been illustrated herein in connection with the testing and selecting of lines, such as those used in telephone systems, it will be understood that this circuit may have a wide number of useful appli- I cations in systems whenever it is desired to utilize a voltage wave for operating responsive devices.

For a better understanding of the cross-bar switches illustrated herein and of the manner in .which these switches are controlled and operated in telephone systems reference is made to the patent to Reynolds, No. 2,021,329 of Novem- 2,093,117 of September 14, 1937.

What is claimed is:

1. The combination in a selective system of a voltage propagating circuit, a plurality of resisber 19, 1935, and to the patent to Carpenter, No.

tors connected in series in said circuit. a source for causing current'to flow through said resistors in series, a single condenser in said circuit chargeable by said current and serving to cause a voltage wave to progress along said series'A of resistors, and a series of responsive devices connected respectively to said resistors, said wave serving to apply an operating voltage to the successive devices as it moves along said resistors.

2. 'Ihe combination in a selective system of a I voltage propagating circuit, a plurality of resistors connected in series in said circuit, a source for causing current to4 ilow through said resistors in series,' a single condenser in said circuit chargeable by said current and serving to cause a voltage wave to progress along said series of resistors, the values of said resistors being selected to obtain a definite relation between the.

voltages at the successive junction points of said resistances, and a series of responsive devices connected respectively, to said junction points, the voltages at the successive junction points risling progressively to the operating value of said devices as the voltage wave is propagated.

3. The combination in a selective system of a' voltage propagating circuit, a -plurality of resistors connected in series in said circuit, a source Aof causing current to flow through said resistors in series, a single condenser in said circuit chargeable by said current and serving to cause a voltage wavejto progress along said series of resistors, the values ,of said resistors being equal to obtain equal voltage dinerences between adjacent resistors, and a plurality of voltage rethe current flowing through said resistors,l and 7,5

serving to cause a progressive reduction in the ilow of said current as it becomes charged, said diminishing current ow serving to cause a voltage Wave to progress along said series of resis-4 tors toward said condenser, and' a series of voltage responsive devices connected .respectively to the `iunction points of said resistors, said Wave serving to apply an operating voltage to the successive devices as it moves along said resistors.

5. The combination in a selective system of a voltage circuit, a plurality of resistors connected in series in said circuit, a source for causing current to flow through said resistors, a condenser in said circuit chargeable by the current iiowing in said resistors and serving to cause a voltage wavevto progress from one resistor to the next, a resistor common to said plurality of resistors for controlling the rate of change of current flow in said circuit as said condenser becomes charged, and a plurality'of responsive devices connected respectively to the resistors of said series, said voltage wave serving to operate said responsive devices.

6. The combination in a selective system of a voltage circuit, a plurality of resistors connected in series in said circuit, a source for causing current to iiow through said resistors, a condenser in said circuit chargeable by the current owing in said resistors and serving to cause a voltage wave to progress from one resistor to the next, a resistor connected in shunt of said condenser for controlling the rate `of change of current in said circuit to maintain auniform time rate of change of the voltages between consecutive resistors in said series, and a plurality of responsive devices connected respectively to the resis tors of said series,l said voltage wave serving to operate said responsive devices.

7. In combinationa group of elements to be selected, a voltage circuit, a plurality of resistors connected in series in said circuit, a series of discharge tubes connected respectively to the successive junction points of said resistors, means for connecting said tubes respectively to the elements of said group, a single condenser connected in said circuit, a source for charging said condenser through said resistors in series to cause a voltage wave to progress along the resistors of said series, said voltage wave serving to apply'an operating voltage to the successive tubes of said series, and means dependent on the condition of any one of the elements of said group for causing the corresponding tube to operate in response to said voltage Wave.

8. In combination, a group of elements to be selected, a voltage circuit, a plurality of resistors connected in series in said circuit, a series of discharge tubes connected respectively to the successive junction points of said resistors, means for connecting said tubes respectively to the elements of` said group, a single condenser connected in said circuit, a source for charging said condenserv through said resistors in series to cause a voltage wave to progress along the resistors of said series, said voltage wave serving to apply an operating voltage to the successive tubes of said series, means dependent on the condition of any one of the elements of said group for causing the corresponding tube to operate in response to said voltage wave, and means eiective when any rent to ow through said resistors, a condenser in said circuit chargeable by the current iiowing in said resistors and serving to cause a voltage i wave to progress from one resistor to'thenext,

impedance means common to' said resistors for' controlling the rate of change of current flow in Asaid circuit to maintain uniform voltage spacings in series in said circuit, a source for causing current to flow through said resistors, a condenser in said circuit chargeable by the current owing in said resistors and servingv to cause a voltage wave to progress from one resistor to the next. inductive means common to said resistors for controlling the rate of change of current iiow in `said 4circuit as the condenser charges to mainvoltage circuit, a plurality of resistors connected tain uniform voltage spacings between consecu- .f tive resistors. and voltage, responsive devices con- 

